Communication devices such as terminals are enabled to communicate wirelessly in a wireless communications system, sometimes also referred to as a cellular radio system or a cellular network. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications system. The RAN is configured to implement one or more RATs.
Terminal are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals, mobile stations, mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some further examples. The user equipments in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity.
The wireless communications system covers a geographical area which is divided into cell areas, wherein each cell area being served by a radio network node such as a Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNB, eNodeB, NodeB, B node, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several radio access and communication technologies. The base stations communicate over the radio interface operating on radio frequencies with the user equipments within range of the base stations.
In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In some RANs implementing one or more RATs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP/GERAN, a user equipment has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. GERAN is an abbreviation for GSM EDGE Radio Access Network. EDGE is further an abbreviation for Enhanced Data rates for GSM Evolution.
In radio communications systems, the radio spectrum is currently and will probably also in the future be a scarce resource. With the introduction of UMTS, new radio spectrum became available, primarily in the 2 GHz band. For some operators the new radio spectrum has been very expensive. Today there are around 10 different frequency bands possible for UMTS deployment, however not all frequency bands are available in every region of the world.
In spite of the number of available frequency bands, the demand for more radio spectrum will very likely lead to so called re-farming (which will be explained below) of already used radio spectrum. This can be seen as a radio spectrum sharing on a very static basis. Most countries in the EU have announced firm plans and timelines for the re-farming of radio spectrum in 900/1800 MHz, the frequency bands typically used for 2G services, such as GSM. Fifteen markets have already implemented re-farming policies while eight others are expected to do so between the years 2011 and 2014. Today the operators have a license to use UMTS in the 900/1800 MHz frequency band, where GSM formerly was the only technique allowed. In some countries, operators have already started re-farming; for example in Finland UMTS is re-farming the 900 MHz.
Furthermore, the same re-farming demand will happen, or already is happening, with LTE. For LTE, the primary frequency band is the 2.6 GHz frequency band in the EU, but elsewhere in the world other frequency bands are used as the primary frequency band. The standard for LTE allows a wide range of frequency bands from 700 MHz to 2.6 GHz, including for example the 1800 MHz frequency band. Thus, it is likely that operators with LTE also will re-farm their existing spectrum such as the 1800 MHz frequency band, sharing frequencies from both their GSM or HSPA frequencies.
By re-farming, when used herein, is meant that base stations for a first RAT is co-sited with base stations for a second RAT. For example, UMTS base stations may be co-sited with GSM base stations, or LTE base stations may be co-sited with UMTS base stations. In fact, it is even possible to share the same Radio Base Station (RBS), e.g. if bought from the same vendor, and share the same Power Amplifier (PA). An example of this is a radio base station which supports different RATs in one and the same radio base station, i.e. a radio base station supporting GSM/EDGE, WCDMA/HSPA and LTE. Note that it is not strictly necessary to utilize the same RBS and PA to perform re-farming between for example LTE and HSPA, especially if it is done on a very static and slow basis.
A problem with existing solutions such as re-farming is that they are static and not based on the current traffic situation. For instance, in a migration scenario, the number of terminals only supporting legacy RATs such as GSM/HSPA, might be large compared to terminals supporting both new RATs, such as LTE, and legacy RATs such as GSM/HSPA, giving indications to allocate a large part of the radio spectrum to the legacy RAT; GSM/HSPA, and less to the new RAT; LTE. Then, the LTE terminals might not be able to utilize their full data rate potential, due to only a small bandwidth, e.g. 5 MHz, allocated to LTE instead of the full bandwidth, e.g. 10 MHz. This will be the case also when the actual number of active HSPA terminals connected to a specific cell is small. Hence static solutions will affect the data rate and may thus reduce user experience for new terminals and/or modems supporting new RATs such as LTE.